Trailex says...Triton Trailers says...
And it's up to the customer to decide which answer makes the most sense.
It's hard to know what to do when you have two "experts" saying the opposite thing! In a case like that it's best to go to a higher source, the tire manufacturers.
Goodyear publishes a load inflation table for their ST and LT trailer tires. They list pressures down to 15 PSI for reduced loads.
Trailex also gets their PSI information from their tire manufacturer.
Greenball and Carlisle publish no such inflation data and therefore have no official recommendations other than what the label says. However, both reps conceded that somewhat less than full pressure would "probably be OK" subject to common sense.
My own (non-expert) opinion is that the pneumatic tire is part of the suspension system. Why revert back to the solid rubber days by making it hard as a rock? Having operated vehicles and equipment with rated tire pressures from 8 PSI to 400 PSI , tire pressure always seemed highly correlated with load supported.
SkiPro makes a good point with his truck tires. Vehicle recommendations depend on application, not not max ratings (which are set by the tire industry for safety reasons). So while the opinion expressed by Triton Trailers' is appreciated and respected with regard to their trailers, I otherwise concur with Trailex (and SkiPro).